The present invention relates to a control system for a semiconductor substrate process line and, more particularly, to a wafer control system for a wafer process wherein semiconductor substrates or wafers are stored in a cassette and processed.
As is well known, the semiconductor device manufacturing process can be roughly divided into two processes: a so-called wafer process, for forming elements in a semiconductor wafer, and a mounting process, for cutting the semiconductor wafer after element formation into chips and sealing the chip in a package. In the wafer process, semiconductor wafers are sliced from a monocrystalline semiconductor ingot, stored in a semiconductor substrate storage cassette (conveyance container) in units of, e.g., 25 pieces, and conveyed to various types of processing units. The type symbol, the lot number, process conditions, and so on of semiconductor wafers are set in units of cassettes. The processing units process in units of cassettes or wafers.
In the conventional wafer process, a type symbol, a lot number and a wafer number are directly marked on each wafer. Alternatively, a cassette number is assigned and a process slip is attached to each cassette, and the cassettes are sequentially conveyed to the processing units. The process slip has a type symbol, a cassette number, a lot number, and a process sequence specific to each lot.
In the latter wafer process, the process slip for lot control is removed from each cassette at the entrance of each processing unit and is stored in a process storage box near the processing unit. After all the wafers in the cassette have been processed, a process slip corresponding to the cassette is selected from the storage box by checking the cassette number, and is reattached to the cassette at the exit of the processing unit. With this system, when the process slip is selected from the storage box, the operator may pick the wrong slip. Thus, a slip that does not correspond to the semiconductor wafers in the cassette is erroneously attached to the cassette. Great confusion results in the wafer process, sometimes causing defective products. In addition, since it takes time to pick out the corresponding slip from the process slip storage box, cassette conveyance in the wafer process is slow, and productivity suffers.